1. Field of the Invention
The present invention relates to a method for manufacturing optical elements and the apparatus therefor. Particularly, the present invention relates to a method for continuously obtaining the optical element having an optically functional surface from the molding material by pressing formation.
2. Related Background Art
In recent years, there has been developed a method for manufacturing the optical element having the optically functional high-precision surface, which requires no machining to finish by grinding, lapping, or the like. The method is implemented in such a manner that an optical element molding material, such as a glass blank preparatory formed in a certain shape with a certain surface precision, is accommodated in a molding die having a predetermined surface precision, and is finished by the pressing formation under heating.
Generally, in a pressing formation method of the kind, an upper molding member and a lower molding member are slidably arranged to face each other in a molding barrel member respectively, and a molding material is introduced into a cavity formed by these upper, lower and barrel members. The molding member is heated to a temperature capable of molding, such as a temperature making the molding material to be of 10.sup.8 -10.sup.12 poise, in a nonoxidizing atmosphere, a nitrogenous atmosphere, for example, in order to prevent the molding member from being oxidized. Then, the molding is closed for pressing for appropriate period of time to transfer the surface shape of the molding member to the surface of the molding material. Subsequently, the temperature of the molding member is lowered to a temperature sufficiently lower than the transition temperature of the glass used as a molding material. Then, after the pressing pressure has been released, the molding member is opened for the delivery of the formed optical element
In this respect, it is possible to heat the molding material preparatorily to an appropriate temperature before being introduced into the inside of the molding member, or introduce the molding material into the inside of the molding member after it has been heated to the molding temperature. Further, it is possible to convey the molding material together with the molding member for a continuous and high-speed molding by performing each process of heating, pressing, and cooling at each of the specific locations.
An optical element pressing formation method and the apparatus therefor, such as set forth above, has been disclosed, for example, in Japanese Patent Laid-Open Appln. No. 58-84134, Japanese Patent Laid-Open Appln. No. 49-97009, British Patent No. 378199, Japanese Patent Laid-Open Appln. No. 63-11529, Japanese Patent Laid-Open Appln. No. 59-150728, Japanese Patent Laid-Open Appln. No. 61-26528, Japanese patent Laid-Open Appln. No 61-44721 and others.
Here in order to perform the aforesaid pressing formation continuously in a small apparatus, there has been proposed (in Japanese Patent Publication No. 63-37044) a method wherein heating stations, pressing stations, cooling stations, and others are arranged on a circle to convey the molding materials and the molded optical elements using a conveying means which is rotatable around the central part of the aforesaid circle and is further provided with expansion arms in the radial direction.
However, in this proposed method, the arms are provided in a number corresponding to the number of stations, and each of the arms always conveys the molding material and the molded optical element to the next station in single steps. Eventually, therefore, the molding material passes through each station.
Consequently, this method is such that the linearly conveying path has simply been made circular, and that the manufacturing speed of the optical element depends on the station which consumes the longest process time of all the stations. Hence, not only is there a restriction in speeding up the manufacturing, but also there is a disadvantage that if trouble occurs at any one of the stations, the operation of the entire system must be suspended immediately. Furthermore, since the arms are provided in a number corresponding the number of stations, the structure becomes complicated.